Contact heater construction



Feb. 20, 1968 H. K. GRAVES CONTACT HEATER CONSTRUCTION- 2 Sheets-Sheet 1 Filed March 29, 1965 F'iG. 2

' INVEN 70 HOWARD K. GRAVES FIG'B Arromvzrs Feb. 20, 1968 H. K. GRAVES ,3

CONTACT HEATER CONSTRUCTION Filed March 29, 1965 '2 Sheet s-Sheet 2 lNVENTOR HOWARD K. G RAVES A T TORNEVS United States Patent ()fifice 3,370,156 Patented Feb. 20, 1968 3,370,156 CONTACT HEATER CONSTRUCTION Howard K. Graves, Cleveland, Ohio, assignor to H. W. Tuttle & Company, Tecumseh, Mich.,'a corporation of Michigan Filed Mar. 29, 1965, Ser. No. 443,243 4 Claims. (Cl. 219540) ABSTRACT OF THE DISCLOSURE A heat exchange construction comprising a strip of conductive metal wrapped transversely to provide a tubular chamber for a heat generating component such as an electrical resistance element, the strip having a plurality of spaced integral fingers on each edge which engage interdigitally and extend in opposite directions substantially tangentially of the tubular chamber to form contact fingers to transmit heat conductively from the unit.

This invention relates to an electrical contact heater and more particularly to that type of heater where an extended electrical resistance unit is disposed relative to a surface in such a way that heat will be transmitted to the surface.

It is an object .of this invention to provide a heater unit which can be applied under tension to the outer wall of a container, as one example, in such a way that a good thermal contact is maintained between the heater and the surface.

Another object of the invention is the provision of a heat transfer element which serves also to sheath and protect a lineal resistance element and which is so designed that pressure against a surface to be heated tightens and strengthens the entire structure.

Another object of the invention is the provision of a contact heater wherein the inherent design of the heat distributing elements assists in the contact thereof with the surface to be heated.

Other objects and features of the invention relating to details of construction and-operation will be apparent in the following description and claims.

Drawings accompany the disclosure and the various views thereof may be briefly described as:

FIGURE 1, a view showing an enclosed circular loop utilizing a preferred embodiment of the design of the present invention.

FIGURE 2, a sectional view on line 22 of FIG- URE 1.

FIGURE 3, a view of the layout of one embodiment of the contact medium prior to shaping.

FIGURE 4, a perspective view showing in detail fastening elements for the ends of the contact strip.

FIGURE 5, an enlarged perspective view showing the details of the contact strip.

FIGURE 6, a longitudinal section illustrating the connection between the resistance element and the terminals of the heater. 7

FIGURE 7, a view of a modified embodiment of a contact strip.

Referring to the drawings, it is an object of the invention to provide a contact heater which has a high thermal contact efiiciency. This is accomplished by providing a strip of conductive material such as metal having a central s'olid portion 20 which is formed as a tube to enclose and protect a heating element 22, this tube having fingers 24 on one side staggered with relation to fingers 26 on the other side as shown in the unformed blank illustrated in FIGURE 3. The completed contact unit is formed, as shown in FIGURES 4 and 5, with the central portion wrapped up into a tube and having the fingers 24 and 26 folded approximately 180 from the blank form position and extending outwardly from the central formed tube 20.

These fingers are preferably formed with a slight angle as shown in dotted lines in FIGURE 2 so that when the device is applied to a circular tank T as shown in FIG- URE l, the fingers are pressed against the walls of the tank under their inherent resilient pressure and thus maintain a tight thermal contact with the wall of the tank. The tank T, for example, might be a condenser wall or any other container which requires heating. The ends of the contact strip are held together by tension brackets 30 (FIGURE 4) which have parallel, spaced base strips 32 which lie alongside the central tube portion 20 and are spot welded to three or four of the end fingers. The plates 32 extend in perpendicular relation to side wings 36 which lie in spaced parallel relation on either side of an integral anchor plate .38 which is apertured to receive both ends of a bolt 42 used to apply tension to the device when disposed in circular fashion as shown in FIGURE 1.

Each of the fingers 24 and 26 forms a discrete point or area of positive contact with the surface being heated and the accumulated total of all of the points of contact provides a high overall efficiency. When the device is formed, the tube 20 is formed around a heating element which is composed of a resistance wire 50 which is wrapped around a fiberglass core 52 and insulated by a sheath 54 of material such as silicon rubber insulation.

Thetubular element 20 is wrapped tightly around the insulator sheath 54 to obtain good thermal contact between the heater and the metallic tube strip. The construction is so designed that when the tubular strip is applied to a surface under tension as shown in FIGURE 1 or in any other manner in which pressure is applied, the fingers 24 and 26 which are normally disposed as shown in the dotted lines of FIGURE 2 with a wide obtuse included angle will be rotated to a common plane as shown in the solid lines of FIGURE 2. This tends to wrap the tube 20 more tightly around the insulator sheath 54 and the greater the pressure that is applied, the tighter is this wrapping contact. The electrical heating element 50 is hermetically sealed by the silicon rubber insulation sheath 54 and thus the conductive tubular strip 20 is provided primarily to conduct the heat away from the element and to provide also mechanical protection for the sheath 54.

In FIGURE 6, a terminal construction is shown wherein each end of the resistance conductor 50 is connected respectively to conductive terminal leads 60 and 62. This is accomplished by exposing a portion 64 of the resistance wire 50 and inserting it into one end of a terminal tube 66 which is recessed to receive this wire, this terminal tube being preferably formed of a conductive material pliable enough that the metal thereof may be crimped around the resistance wire 64 and also around the ends of the conductive elements 60 andv 62 at the other end of the terminal unit. The exposed terminal unit is then covered by an insulated potting material 68 to fill in between the insulating sheath 54 and an insulating cover 70 on the lead wires 60 and 62. Thus, a positive contact is made between the ends 64 of the resistance element 50 and the respective lead wires 60 and 62.

Another embodiment of the invention is shown in FIG- URE 7 wherein the core heater is encased in a tube formed with tangential flanges 82 and 84 spot welded together each flange having contiguous wings 86 separated by slits 88. Here again, the wings are initially set at a slight angle (large included obtuse angle) to allow some bending as the contact heater is applied. The end construction can be the same as shown in FIGURES 4 and 6.

In each case the fingers are disposed in relation to the elongate enclosing portion of the unit so that they are olfset from parallel planes which include the enclosing portion and extend in the general direction of the fingers. Thus, moving the unit toward a surface causes positive finger contact and insures good thermal conduction.

What is claimed as new is:

1. A contact heater strip comprising:

(a) an electrical resistance element adapted to be con- 'nected in an electrical circuit and covered with an insulative sheath,

(b) a conductive metallic contact element comprising an elongate central section wrapped transversely to provide a tubular enclosure for said sheath and having on one side laterally extending fingers spaced and alternated with laterally extending fingers on the other side, each finger on one side extending into the space between adjacent fingers on the other side in interdigital relation.

2. A contact heater strip comprising:

(a) an electrical resistance element adapted to be connected in an electrical circuit and covered with an insulative sheath,

(b) a conductive metallic contact element comprising an elongate central section wrapped transversely to provide a tubular enclosure for said sheath and having on one side laterally extending fingers spaced and alternated with laterally extending fingers on the other side, each finger 'on one side extending into the space between adjacent fingers on the other side in interdigital relation, said fingers being disposed to include a large obtuse angle in an at rest position whereby to contact resiliently at surface against which the heater strip is pressed.

3. A contact heater strip for enclosing an electrical resistance element which comprises a strip of conductive metal shaped in a transverse dimension in the form of a tube to form an elongate chamber to enclose a resistance element, and, on each edge of the strip integrally therewith, laterally extending fingers alternately spaced on each side interlocking interdigitally and extending in opposite directions from said tube and generally tangential thereof to form heat conduction fingers for the transmission of heat from said tube.

4. A contact heater strip as defined in claim 3 in which the opposed fingers are disposed to include a wide obtuse angle wherein said fingers will have resilient contact with a face against which said strip is pressed.

References Cited UNITED STATES PATENTS 1,494,939 5/1924 Abbott 219540 2,019,913 11/1935 Kotr-baty 219--540 2,140,442 12/ 1938 Clark 24827 2,236,496 4/ 1941 Beggs 24827 2,786,125 3/1957 Drugmand et al. 219535 2,809,004 10/ 1957 Kaufman et al 248300 2,852,594 9/1958 Amand 17435 2,882,376 4/1959 Charbonneau 219--530 2,434,519 1/ 1948 Raskin 165181 2,715,518 8/1955 Bickler 165185 2,807,659 9/1957 Woods 165-185 FOREIGN PATENTS 73,461 12/ 1951 Denmark. 1,015,925 8/ 1952 France. 1,171,511 1/1959 France.

RICHARD M. WOOD, Primary Examiner.

VOLODYMYR Y. MAYEWSKY, Examiner. 

